A bladed rotor, such as the fan rotor of a gas turbine engine, includes a central hub and a quantity of blades secured to and projecting radially outward from the hub. The rotor rotates about a longitudinal central axis. Because of nonuniform distribution of mass in the hub and blades, it is nearly impossible to achieve perfect balance for a bladed rotor. Nevertheless, minimizing rotor imbalance is essential for limiting vibration and noise during operation of the rotor. A rotor is considered to be balanced when its imbalance is no greater than a predetermined amount.
In cases where one or more unserviceable blades on a rotor are to be replaced by replacement blades, the rotor will usually require rebalancing since the replacement blades usually have a mass distribution different from that of the unserviceable blades. One way to rebalance the rotor has been to replace blades in pairs, the replacement blades of each pair having approximately equal mass distributions and being placed substantially 180 degrees opposite each other on the hub. The main drawback of this approach is that a perfectly serviceable blade is replaced along with the unserviceable blade. In the case of modern gas turbine engine fan rotors, the blades are expensive and replacing a serviceable blade is not cost effective.
A more attractive way to rebalance the rotor is to replace only the unserviceable blade and to rearrange at least some of the blades to restore the balance of the rotor. One well known prior art method for identifying how to rearrange the blades is known as simulated annealing. Simulated annealing exhibits good performance in identifying arrangements for reducing rotor imbalance. However simulated annealing examines a great many possible blade arrangements and frequently identifies arrangements in which many, if not most, of the blades are relocated from their initial locations to new target locations. Thus, simulated annealing entails considerable analysis to identify an acceptable blade arrangement. Moreover, the physical effort and time required to remove large numbers of blades from their initial locations and reinstall each of them in a new target location can be significant.
In view of the foregoing, a method of balancing a bladed rotor which limits the need for extensive analysis and physical effort is sought.